Replacement of sulphur in methionine of protein with selenium has been widely used for protein structure determination by X-ray crystallography, where selenium serves as a scattering center for multi-wavelength anomalous dispersion (MAD) [W. A. Hendrickson, J. R. Horton, D. M. LeMaster, EMBO. J. 1990, 9, 1665-1672; W. A. Hendrickson, Science 1991, 254, 51-58; W. A. Hendrickson, Trends. Biochem. Sci., 2001, 25, 637-643]. Recently selenium has been introduced into several different positions of DNAs and RNAs, including the 5′ [N. Carrasco, D. Ginsburg, Q. Du, Z. Huang, Nucleosides, Nucleotides, Nucleic Acids 2001, 20, 1723-1734], 2′ [Q. Du, N. Carrasco, M. Teplova, C. J. Wilds, M. Egli, Z. Huang, J. Am. Chem. Soc. 2002, 124, 24-25; N. Carrasco, Y. Buzin, E. Tyson, E. Halpert, Z. Huang, Nucleic Acids Res. 2004, 32, 1638-1646; J. Jiang, J. Sheng, N. Carrasco, Z. Huang, Nucleic Acids Res. 2007, 35, 477-485; J. Sheng, J. Jiang, J. Salon, Z. Huang, Org. Lett. 2007, 9, 749-752; C. Hobartner, R. Micura, J. Am. Chem. Soc. 2004, 126, 1141-1149; H. Moroder, C. Kreutz, K. Lang, A. Serganov, R. Micura, J. Am. Chem. Soc. 2006, 128, 9909-9918] and 4′ [L. S. Jeong, D. K. Tosh, H. O. Kim, T. Wang, X. Hou, H. S. Yun, Y. Kwon, S. K. Lee, J. Choi, L. X. Zhao, Org. Lett. 2008, 10, 209-212; J. K. Watts, B. D. Johnston, K. Jayakanthan, A. S. Wahba, B. M. Pinto, M. J. Damha, J. Am. Chem. Soc. 2008, 130, 8578-8579] positions of the ribose, the phosphate backbone [C. J. Wilds, R. Pattanayek, C. Pan, Z. Wawrzak, M. Egli, J. Am. Chem. Soc. 2002, 124, 14910-14916; N. Carrasco, J. Caton-Williams, G. Brandt, S. Wang, Z. Huang, Angew. Chem. Int. Ed. Engl. 2006, 45, 94-97; G. Brandt, N. Carrasco, Z. Huang, Biochemistry 2006, 45, 8972-8977] and the nucleobases [J. Salon, J. Sheng, J. Jiang, G. Chen, J. Caton-Williams, Z. Huang, J. Am. Chem. Soc. 2007, 129, 4862-4863; J. Caton-Williams, Z. Huang, Angew. Chem. Int. Ed. Engl. 2008, 47, 1723-1725; J. Salon, J. Jiang, J. Sheng, O. O. Gerlits, Z. Huang, Nucleic Acids Res. 2008, 36, 7009-7018].
As a chalcogen element, tellurium follows sulfur and selenium in elemental group VI of the periodic table. Tellurium has a larger atomic radius (1.35 Å), compared with selenium (1.17 Å) and sulfur (1.04 Å), and has higher metallic property and stronger electron delocalizability. An electron-rich tellurium atom will likely donate electron and facilitate electron delocalization when it is introduced into DNA duplexes via nucleobases, which are relatively electron-deficient. Probably due to its metallic property and weak covalent bonds with carbon and hydrogen [L. Moroder, J. Pept. Sci. 2005, 11, 187-214], so far, no tellurium functionality has been discovered in any natural biological molecules. However, tellurium was successfully incorporated into proteins in 1989 through Te-resistant fungi grown in the presence of tellurite on a sulphur-free medium [S. E. Ramadan, A. A. Razak, A. M. Ragab, M. el-Meleigy, Biol. Trace Elem. Res. 1989, 20, 225-232]. Later, the Te-methionine derivatization for protein structure determination was investigated and developed. Boles and co-workers reported the expression of telluromethionine (TeMet) dihydrofolate reductase in 1994 [J. O. Boles, K. Lewinski, M. Kunkle, J. D. Odom, B. Dunlap, L. Lebioda, M. Hatada, Nat. Struct. Biol. 1994, 1, 283-284], and the Te-incorporation technique was further optimized to efficiently introduce TeMet into several proteins [N. Budisa, W. Karnbrock, S. Steinbacher, A. Humm, L. Prade, T. Neuefeind, L. Moroder, R. Huber, J. Mol. Biol. 1997, 270, 616-623]. Furthermore, the Te-protein stability under X-ray radiation and the isomorphism of the Te-proteins were confirmed, and more tellurium chemistry has also been developed [N. Budisa, B. Steipe, P. Demange, C. Eckerskorn, J. Kellermann, R. Huber, Eur. J. Biochem. 1995, 230, 788-796; M. Farina, F. A. Soares, G. Zeni, D. O. Souza, J. B. Rocha, Toxicol. Lett. 2004, 146, 227-235; W. Karnbrock, E. Weyher, N. Budisa, R. Huber, L. Moroder, J. Am. Chem. Soc. 1996, 118, 913-914].
The nucleobases play the most critical roles in duplex recognition of nucleic acids. Well-behaved base-pair recognition and sequence-dependent specificity of DNAs and RNAs have stimulated extensive research investigations, such as DNA nano-structure construction and self-assembling [a) J. Zheng, J. J. Birktoft, Y. Chen, T. Wang, R. Sha, P. E. Constantinou, S. L. Ginell, C. Mao, N. C. Seeman, Nature 2009, 461, 74-77. b) E. S. Andersen, M. Dong, M. M. Nielsen, K. Jahn, R. Subramani, W. Mamdouh, M. M. Goias, B. Sander, H. Stark, C. L. Oliveira, J. S. Pedersen, V. Birkedal, F. Besenbacher, K. V. Gothelf, J. Kjems, Nature 2009, 459, 73-76. c) P. W. Rothemund, Nature 2006, 440, 297-302. d) X. Xue, F. Wang, X. Liu, J. Am. Chem. Soc. 2008, 130, 3244-3245], disease and pathogen detection at single molecule level [A. Singer, M. Wanunu, W. Morrison, H. Kuhn, M. Frank-Kamenetskii, A. Meller, Nano. Lett. 2010, 10, 738-742], oligonucleotide drug discovery [K. Tiemann, J. J. Rossi, EMBO Mol. Med. 2009, 1, 142-151], and nanoelectronic device design based on DNA conductivity and charge migration [a) Y. C. Huang, D. Sen, J. Am. Chem. Soc. 2010, 132, 2663-2671. b) I. Kratochvilova, K. Kral, M. Buncek, A. Viskova, S. Nespurek, A. Kochalska, T. Todorciuc, M. Weiter, B. Schneider, Biophys. Chem. 2008, 138, 3-10. c) T. Ito, S. E. Rokita, Angew. Chem. Int. Ed. 2004, 43, 1839-1842. d) R. N. Barnett, C. L. Cleveland, A. Joy, U. Landman, G. B. Schuster, Science 2001, 294, 567-571. e) D. Porath, A. Bezryadin, S. de Vries, C. Dekker, Nature 2000, 403, 635-638. f) H. W. Fink, C. Schonenberger, Nature 1999, 398, 407-410]. Moreover, chemical modifications of nucleobases have been widely used to selectively tailor the biochemical and biophysical properties of DNAs and RNAs and to probe their biochemical and biological mechanisms, including base-pairing specificity, polymerase recognition, and DNA damaging and repairing [a) Z. Yang, F. Chen, S. G. Chamberlin, S. A. Benner, Angew. Chem. Int. Ed. 2010, 49, 177-180. b) M. Egli, P. S. Pallan, Chem. Biodivers. 2010, 7, 60-89. c) A. E. Hassan, J. Sheng, W. Zhang, Z. Huang, J. Am. Chem. Soc. 2010, 132, 2120-2121. d) J. C. Delaney, J. Gao, H. Liu, N. Shrivastav, J. M. Essigmann, E. T. Kool, Angew. Chem. Int. Ed. Engl. 2009, 48, 4524-4527. e) M. Ljungman, Chem. Rev. 2009, 109, 2929-2950. f) A. M. Sismour, S. A. Benner, Nucleic Acids Res. 2005, 33, 5640-5646. g) T. W. Kim, J. C. Delaney, J. M. Essigmann, E. T. Kool, Proc. Natl. Acad. Sci. USA 2005, 102, 15803-15808]. Furthermore, the conductivity of DNAs has been studied extensively via nucleobase modification, metallization and conjugating with conductive nanoparticles or polymers through scanning tunneling microscopy (STM) imaging [I. Kratochvilova, K. Kral, M. Buncek, A. Viskova, S. Nespurek, A. Kochalska, T. Todorciue, M. Weiter, B. Schneider, Biophys. Chem. 2008, 138, 3-10; a) E. Braun, Y. Eichen, U. Sivan, G. Ben-Yoseph, Nature 1998, 391, 775-778. b) J. L. Coffer, S. R. Bigham, X. Li, R. F. Pinizzotto, Y. G. Rho, R. M. Pirtle, I. L. Pirtle, Appl. Phys. Lett. 1996, 69, 3851-3853. c) Y. F. Ma, J. M. Zhang, G. J. Zhang, H. X. He, J. Am. Chem. Soc. 2004, 126, 7097-7101. d) X. Guo, A. A. Gorodetsky, J. Hone, J. K. Barton, C. Nuckolls, Nat. Nanotechnol. 2008, 3, 163-167. e) B. Elias, F. Shao, J. K. Barton, J. Am. Chem. Soc. 2008, 130, 1152-1153].
Therefore, there is a need existing for the identification of new Te-nucleoside phosphoramidites and Te-modified oligonucleotides, and their derivatives in DNAs, RNAs and modified nucleic acids.